A large variety of power plants generate power by the expansion of a hot, pressurized working fluid or gas which is harnessed mechanically to provide mechanical motion to convey the power to a load to perform useful work. Dependent upon the type, such power plants utilize mechanisms which operate by and large on well known cycles such as the Otto cycle, Diesel cycle and many other lesser known cycles, and involve compression of the working fluid and the addition of heat thereto prior to the expansion of the working fluid. In the usual case, the addition of heat is accomplished by the burning of fuel which, in the case of Otto and Diesel cycle mechanisms is accomplished within a working chamber within a positive displacement mechanism or, in the case of, for example, the Stirling cycle, externally but in close adjacency to a working chamber of a positive displacement mechanism.
Even before humanity's attention was focused on the very real need for the conservation of energy that has become apparent in recent years, there evolved many proposals for increasing the efficiency of such mechanisms in any of a variety of ways. For example, in conventional single stage Otto cycle mechanisms, the working fluid or gas is never fully expanded to a point whereat its pressure would equal the ambient pressure. Rather, the partially expanded working fluid would be literally dumped to atmosphere by the opening of a valve or a port at which time it would fully expand but perform no useful work in the process. Consequently, turbochargers and compound engines evolved wherein the partially expanded gas was not dumped directly to atmosphere, but rather, to an additional expander mechanism which would utilize at least some of the energy remaining in the partially expanded gas before allowing it to escape to atmosphere. In the case of turbochargers, the gas is utilized to drive a compressor to pre-compress the working fluid before entering the positive displacement mechanism on the succeeding cycle. In the case of compound engines, the gas is directed to a turbine for further expansion, which turbine frequently would be mechanically linked to the output shaft of the positive displacement mechanism.
Such proposals did in fact result in the recovery of more energy from the fuel and provide for greater efficiency of operation. However, it soon became apparent that additional losses were present in the form of so-called "blow down" losses which are due to pressure loss that occurs, without the performance of useful work, when the partially expanded gas is released in the working chamber of a positive displacement mechanism at a pressure greater than the inlet pressure of the second stage expander as the turbocharger or turbine. Consequently, there have evolved proposals for minimizing or avoiding blow down losses as, for example, that illustrated in U.S. Pat. No. 3,961,484 issued June 8, 1976 to Harp. Again, improved efficiency will result but even assuming that blow down losses are eliminated entirely in such proposals, energy is still lost in that while the working fluid is expanded all the way down to atmospheric pressure and performing work all the while, its temperature at atmospheric pressure will remain elevated above ambient temperature. The energy content of the fully expanded working fluid in the form of the heat retained thereby is, of course, lost. The present invention is directed to overcoming one or more of the above problems.